As inspection of states (corrosion, cracks, cavity formation, or such) of structures or components, a visual inspection, a hammering test, an ultrasonic inspection (echo inspection) and such have been applied so far. The visual inspection and the hammering test are, however, likely to cause variations in inspection results depending on skill levels of inspectors, and inherently have limited inspection accuracy. These inspection methods are, in addition, applicable only to parts where workers can observe or hammer. While the ultrasonic inspection may not cause issues led from artificial inspection as discussed above, there is a difficulty in determination of locations.
There are proposed some inspection methods having accuracy, which utilize radiation. The non-patent literature as described below discloses an analysis method using a prompt gamma ray. The term “prompt gamma ray” generally means a ray emitted by a nuclear reaction within a very short time, but is herein particularly defined as a gamma ray emitted just after trapping of an epithermal neutron by resonance absorption.